Collecting and sending soil samples to a laboratory

A laboratory can analyse the material in a container, but it cannot reconstruct an undocumented depth, identify a mixed-up bag or recover the original locations after unrelated soil has been combined.

Use the sampling plan and the receiving laboratory’s instructions together. The plan says where and why to collect; the laboratory specifies what material it needs and how that material must be handled for the requested analyses.

Confirm the collection instructions before departure

Prepare one field sheet for each sampling unit. Include the field and zone reference, sample ID, intended analyses, required depth, increment count, container and handling instructions. Download maps for offline use if connectivity is uncertain.

Confirm that the instructions apply to the crop, soil and region. Teagasc’s Irish fertility guidance, for example, describes a 10 cm depth and at least 20 cores for its routine sampling approach. Those figures illustrate a complete regional procedure; they should not be copied automatically into a different laboratory programme. Read the Teagasc guidance.

If the order includes analyses with incompatible preparation requirements, arrange separate samples or laboratory-approved splitting. Do not assume a bag prepared for routine fertility can also support every biological or specialist test.

Pack for identification as well as collection

Alongside the appropriate corer or sampling tool, pack clean mixing equipment where compositing is required, the laboratory’s containers, durable labels, submission forms and a way to record actual collection. Include cleaning supplies appropriate to the method and sufficient spare containers for damaged packaging or separately investigated areas.

Check that labels remain readable in the expected conditions. A printed ID that comes off a damp bag is less useful than a simple, durable mark. Keep the submission paperwork protected from soil and moisture, and retain a copy before dispatch.

Use a short departure check: correct map, correct procedure, correct containers, unique IDs, working recording equipment and agreed delivery arrangements. This prevents the field team from improvising key decisions halfway through the visit.

Confirm the sampling area on arrival

Compare the map with actual conditions. Look for unexpected access restrictions, standing water, recently disturbed ground or differences that were absent from the planning information. Record them before changing the route.

For routine area-average fertility sampling, unusual spots may need separate treatment instead of inclusion in a general composite. Oklahoma State University explains why atypical locations and fertiliser bands can distort a routine result. When investigating an unusual spot deliberately, identify it as a separate diagnostic sample rather than simply omitting it from the investigation. See the OSU sampling guide.

If a planned random location cannot be sampled, follow the approved replacement procedure. Record the unavailable location and reason. Choosing a convenient nearby position without recording the change makes the final dataset harder to interpret.

Collect at the specified depth and keep units separate

Use the tool consistently and check depth throughout the job. Where the procedure defines separate depth intervals, keep each interval separate and label it clearly. Do not top up a shallow sample with deeper material just to fill the container.

For a composite, collect the specified increments across its designated area, following the chosen protocol. Keep soil from different sampling units in separate batches. Clean tools and mixing equipment between units as required, particularly when moving from an unusual or potentially contaminated area.

University of Maryland Extension describes collecting multiple cores and mixing them before taking a laboratory subsample. It also directs users to the receiving laboratory for submission requirements. Its quantities and depths are guidance for that context, rather than universal instructions. Read the collection guide.

Record what actually happened: completed increments, actual depth, date, collector and deviations. A plan with 20 intended locations is not evidence that all 20 were visited. If collection is incomplete, retain that fact with the sample.

Mix and subsample only when the method requires it

For an approved composite procedure, use clean equipment to combine the intended increments thoroughly before taking the required submission portion. Avoid selecting only the easiest or finest material from one part of the mixture.

Do not composite independent samples that the study needs to analyse separately. Do not combine different depths or merge a weak patch with a comparison area unless that combination was explicitly part of the design.

Finish collecting for one sampling area and seal its containers before beginning another. Check its label against the field sheet, record the container count and clear the mixing area. This reduces opportunities for an unidentified container to remain beside the next batch.

Follow test-specific preservation and delivery instructions

There is no single correct preparation rule for every soil test. Some routine procedures use dried soil; other measurements depend on preserving a different sample condition. Ask the laboratory about time, temperature, drying, refrigeration, freezing and packaging for the exact order.

For example, the University of Minnesota provides specific immediate-handling instructions for nitrate samples. These differ from treating a bag of soil as stable material that can wait indefinitely for dispatch. Follow the receiving laboratory’s current instructions rather than borrowing a heating or freezing method from another service. See its sample-information instructions.

Soil-health investigations can have different needs again. NRCS provides dedicated guidance for field sampling and laboratory submission for soil-health testing. Confirm that the selected procedure covers your requested indicators. See the NRCS soil-health resources.

Reconcile the shipment before handing it over

Compare the physical containers with the submission sheet and field record. Every container should have one unambiguous identity; every submitted ID should have a corresponding collection record. Flag incomplete sampling, unusual conditions or deviations for laboratory and adviser review.